1. Field of the Invention
The proposed invention relates to a method for integrating anti-reflection layer and salicide block, and more particularly to a method for simplifying fabricating process of a photodetector device.
2. Description of the Prior Art
Because advancement of semiconductor technology and gradually increased requirement of high-integrated device, importance of device that includes several different functional elements is increased, such as the photodetector device that includes photodiode and transistor. However, because any specific functional element corresponds to a specific structure and a specific fabricating process, inconsistent difficulties is unavoidable during integration of different elements, especially when structure of any element is complex, such as complementary metal-oxide semiconductor. A popular solution of the difficulty is to divide the whole device into several independent parts and then forms each part separately. For instance, a chip is divided into several parts and when any specific part is formed photoresist is used to cover other parts. Obviously, unavoidable disadvantages of the method comprise prolonged cycle time and increased wastage of interactants.
In terms of photodetector device that usually used by digital camera and scanner, as the basic structural illustration shown in FIG. 1A, photodetector device is formed on substrate 10 and comprises sensor area 11 and transistor area 12. Herein, several isolations 102 locate on substrate 10, some doped regions 101 locate in sensor area and are separated to each other by some isolations 102, and there are transistors made of gates 121, sources 122, drains 123 and spacers 124 locate in transistor area. And silicide 125 locates on gates 121, sources 122 and drains 123. Beside, dielectric layer 13 locates on substrate 10 and covers all forementioned structures, interconnects 14 locates on dielectric layer 13 and further connecting with transistors, covering layer 15 locates on dielectric layer 13 and totally covers interconnects 14, and color filter 16 locates on covering layer 15 and over doped regions 101. Further, because that color filter 16 is used to let only some specific light propagate to specific doped regions 101, not only at least one color filter locates over anyone of doped regions 101, but also no lighttight structure, such as interconnects 14 locates between a doped region 101 and corresponding color filter 16.
However, in sensor area 11, because that light propagates through color filters 16 to doped regions 101 will be partly reflected and also owing to the truth that light does not always vertically propagate to doped regions 101, reflected light will be distributed in all directions. Significantly, as reflected light is reflected by lighttight interconnects 14, it is possible that any doped region 101 is interfered by other doped regions 101 and then crosstalk phenomena is happened. It means that any doped region 101 can not distinguish received light is the light propagated from corresponding color filter 16 or the light propagated from neighboring interconnects 14 which only is noise. Therefore, as FIG. 1B shows, to make sure any doped region 101 is not interfered by light that is reflect by other doped regions 101, it is necessary to form anti-reflection layer 17 on all doped regions 101 before dielectric layer 13 is formed. As usual, available materials of anti-reflection layer 17 are TiN, Ti or TiW.
On the other hand, in transistor area 12, importance of silicide 125 is increased as critical scale is decreased, but it is not desired to cover total transistor area 12 by silicide 125. That is to say, it is necessary to form salicide block 18 on substrate 10 and cover forbidden region of transistor area 12 before silicide 125 is formed, as FIG. 1B shows, where forbidden region is the region that silicide 125 is needless. In general, material of salicide block 18 will not react with metal for forming silicide 25, and available materials comprise tetraethyl-orthosilicate (TEOS).
According to previous discussion, it is natural that because material of anti-reflection layer 17 is different to material of salicide block 18, though doped regions 101 and isolations 102 of both areas can be formed together to simplify the fabricating process of photodetector device, but following processes of different areas can not be formed at the same time until silicide 125 is formed. However, referring to FIG. 1B, due to the structural difference of the two areas, some processes for constructing these different structures are always incompatible, such as process for forming gate 121, process for forming silicide 125 and process for forming color filter 16. But due to location of anti-reflection layer is similar to location of salicide block 18, it is possible to integrate process for forming anti-reflection layer 17 and process for forming salicide block 18. Thus, how to overcome current difficulties to properly integrate these processes is an important field of fabrication processes of photodetector device.